David M. Watson

Charles Sturt University, Бэтхерст, New South Wales, Australia

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Publications (54)142.94 Total impact

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    Simon J Watson · Gary W Luck · Peter G Spooner · David M Watson

    Full-text · Dataset · Jan 2016
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    David M Watson
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    ABSTRACT: Insectivorous birds have been recognized as disproportionately sensitive to land-use intensification and habitat loss, with those species feeding primarily on the ground exhibiting some of the most dramatic declines. Altered litter inputs and availability of epigeic arthropods have been suggested to underlie reduced abundances and shrinking distributions but direct evidence is lacking. I used a patch-scale removal experiment in southern Australia to evaluate whether ground-feeding insectivores are especially vulnerable to altered litter-fall. Building on work demonstrating the importance of mistletoe litter to nutrient dynamics, litter was reduced by removing mistletoe (Loranthaceae) from one set of eucalypt woodlands, responses of birds three years after mistletoe removal compared with otherwise similar control woodlands containing mistletoe. Despite not feeding on mistletoes directly, insectivores exhibited the greatest response to mistletoe removal. Among woodland residents, ground-foraging insectivores showed the most dramatic response; treatment woodlands losing an average of 37.4% of their pre-treatment species richness. Once these 19 species of ground-foraging insectivores were excluded, remaining woodland species showed no significant effect of mistletoe removal. This response reflects greater initial losses in treatment woodlands during the study (which coincided with a severe drought) and double the number of species returning to control woodlands (where mistletoe numbers and litter were not manipulated) post-drought. These findings support the productivity-based explanation of declining insectivores, suggesting diminished litter-fall reduced habitat quality for these birds via decreased availability of their preferred prey. In addition to altered prey availability, interactions between litter-fall and epigeic arthropods exemplify the importance of below-ground / above-ground linkages driving ecosystem function.
    Preview · Article · Dec 2015 · PLoS ONE
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    David M. Watson · Maggie J. Watson
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    ABSTRACT: In most urban and agricultural landscapes, remnants of native vegetation are surrounded by an inhospitable matrix. Although vagile species come and go, many reptiles, amphibians and small mammals are effectively stranded and declining towards local extinction. In the same landscapes, other areas where these species are absent are improving in habitat quality, both through natural regeneration and active restoration efforts. So, for many species in many domesticated landscapes, there are too many individuals in some patches of decreasing quality and no individuals in patches of increasing quality. One solution to this situation is to move animals from those areas where there are plenty to suitable areas where there are none. These targeted translocations apply lessons learned from revegetation to dispersal-limited animals to in-fill distributional ranges, increase population size and improve both demographic and genetic connectivity, pushing nonequilibrial metapopulations away from extinction via an imposed mass effect. In contrast to conventional reintroduction schemes-expensive, reactive interventions involving highly-trained specialists and captive-raised endangered species-these inexpensive, proactive, community-driven initiatives aim to avert future declines by keeping common species common. Having introduced the wildlife restoration vision, we use two scenarios to illustrate the benefits of the approach-to species, ecosystem function, ecological understanding, restoration practise and public engagement. As well as adhering to best-practise reintroduction techniques to ensure animal welfare is not compromised and avoid detrimental effects to source populations or release sites, we emphasize community participation, data quality and long-term accessibility as paramount to maximize learning opportunities.
    Full-text · Article · Sep 2015 · Biological Conservation
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    David M Watson · Susan E Anderson · Valerie Olson

    Full-text · Dataset · Feb 2015
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    David M Watson · Susan E Anderson · Valerie Olson

    Full-text · Dataset · Feb 2015
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    David M Watson · Susan E Anderson · Valerie Olson
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    ABSTRACT: Reproductive investment is typically considered in terms of size and number of propagules produced. Compared with a thorough understanding of the overall patterns and ecological correlates of avian clutch size, egg size has received less attention and the total effort invested in laying a clutch of eggs is rarely considered. We used clutch volume as an alternative estimate of reproductive investment and present the first class-level analysis of clutch volume in birds using 1,364 randomly-selected species in 204 families. The relationship between body mass and egg volume was very strong (r2 = 0.946), validating previous studies identifying four families (Apterygidae, Pelecanoidiididae, Sternidae and Dromadidiae) with disproportionately large eggs. Clutch volume was also closely related to body mass (r2 = 0.909) and all but one of the taxa with disproportionately large eggs conformed to the overall relationship, their greater egg dimensions compensated by diminished clutch size. The only family which departed significantly from the relationship between body mass and clutch volume was the mound builders (Megapodiidae)-the only group of birds that do not rely on body heat for incubation. Although previously known for laying large clutches of large eggs containing disproportionately large yolks, the remarkable investment of megapodes in reproduction (more than seven times greater than other birds of comparable mass) has been hitherto overlooked. We consider the evolutionary basis and ecological implications of this finding, suggesting that energetic costs associated with incubation act as an upper limit on reproductive output of other birds. We recommend clutch volume as a sensitive, fine-grained measure of reproductive effort for research at a wide range of scales and advocate further analysis of ecological correlates of clutch volume in birds and amniotes generally.
    Full-text · Article · Jan 2015 · PLoS ONE
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    Anna E Burns · Gary S Taylor · David M Watson · Saul A Cunningham
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    ABSTRACT: This study is the first direct comparison of the diversity of phytophagous insects associated with a parasitic plant and its host plants. Specifically, we compared the species composition, density and host specificity of psylloids or jumping plant lice (Hemiptera: Psylloidea), inhabiting hemiparasitic box mistletoe Amyema miquelii, and three of its host Eucalyptus species: Eucalyptus blakelyi, Eucalyptus melliodora and Eucalyptus polyanthemos. Insects were sampled by restricted canopy fogging in remnant Eucalyptus woodlands in an agricultural region of temperate south-eastern Australia. Although most psylloids are understood to be mono- or oligophagous, most species in our survey were found on the foliage of both mistletoes and eucalypts. Nevertheless, analysis of density patterns and reference to previous work on psylloids supports the high degree of host specificity for psylloids, leading to distinct assemblages on these two intimately associated plants. We show that (1) there were two mistletoe-associated species of psylloid and 18 eucalypt-associated species; (2) there were a large number of tourist species, as indicated by known psylloid/plant host associations; and (3) psylloid density was higher on eucalypt than mistletoe leaves. The different psylloid assemblages found on box mistletoes compared with their host plants are likely to be due to differences in the foliar properties implicated in host specificity and host selection by phytophagous insects. Further research is required to understand the ecological dynamics and evolutionary origins of these arboreal assemblages.
    Full-text · Article · Nov 2014 · Austral Entomology
  • Emma Razeng · David M. Watson
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    ABSTRACT: Food availability is emerging as a key determinant of avian occurrence and habitat use in a variety of systems, but insectivores have received less attention than other groups and the potential influence of nutritional quality has rarely been considered. Rather than a uniform food source, arthropods vary greatly in terms of nutritional composition, but does this variation translate into differential consumption? Building on previous work that demonstrated clear preference for some arthropod groups by 13 species of ground-foraging insectivores, we compare the nutritional composition of these arthropod groups with other groups commonly encountered but seldom consumed in the same habitat types. Using samples of arthropods collected from a eucalypt woodland in southern Australia, we found the high frequency prey groups (Coleoptera, Lepidoptera, Orthoptera and Araneae) consistently contained higher fractions of crude protein and total fat than the low frequency groups (Diptera, Hymenoptera and Odonata). Even more clear-cut differences were noted in terms of micronutrients; high frequency prey containing significantly greater concentrations of seven elements than low frequency prey and significantly greater amounts per individual arthropod for all eleven elements measured. These results indicate that the nutritional quality plays an important role in prey selection in insectivores and suggests that micronutrients may be more important determinants of prey choice than previously recognized. Integrating these findings with previous work suggesting food limitation may constrain distribution patterns of birds in fragmented landscapes, we contend that variation in nutritional quality helps explain observed patterns in insectivore diets and occurrence. In addition to explaining why smaller and more disturbed habitats are unable to support resident insectivore populations, this bottom-up mechanism may underlie the disproportionate sensitivity of insectivores to land-use intensification.
    No preview · Article · Sep 2014 · Journal of Avian Biology
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    Simon J. Watson · David M. Watson · Gary W. Luck · Peter G. Spooner
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    ABSTRACT: The extent and connectivity of individual habitat types strongly affects the distribution and abundance of organisms. However, little is known of how the level of connectivity and the interactions between different habitat types influences the distribution of species. Here, we used the geographically restricted and endangered regent parrot Polytelis anthopeplus monarchoides as a case study to examine the importance of composition and connectivity between different elements in 39 complex landscape mosaics (each 10 km radius). We compiled a database of 674 regent parrot nesting records, regional vegetation maps and measures of multipath connectivity between core vegetation types under different scenarios of resistance to movement provided by landscape elements. The occurrence of regent parrot nests was strongly affected by landscape composition, being positively related to the extent Eucalyptus camaldulensis riverine forest, but negatively related to the extent of semi-arid woodlands dominated by Eucalyptus largiflorens. Connectivity between E. camaldulensis forest (principal nesting habitat) and mallee (preferred feeding habitat) was a strong predictor of nest locations. Our study shows that the suitability of fragmented agricultural landscapes for supporting species can be greatly affected by connectivity and interactions between preferred and non-preferred habitats. For species that require complementary habitats such as the regent parrot, conservation management activities may be ineffective if they simply focus on a single core habitat type or the impacts of human land uses without regard to the interrelationships among landscape elements. While increasing the amount of primary preferred habitat should remain a cornerstone goal, increasing the extent and improving connectivity with alternative landscape elements also should be priority management objectives.
    Full-text · Article · Jul 2014 · Landscape Ecology
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    Simon J Watson · Gary W Luck · Peter G Spooner · David M Watson
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    ABSTRACT: The frequency and extent of human-induced land-cover changes is escalating worldwide. Recurrent turnover of land-cover types will affect ecosystems over and above major, one-time changes (eg deforestation). Here, we show how a deeper appreciation of the temporal dynamics of land-cover change is needed to understand its effects on ecosystems. We distinguish between four key components of land-change regimes: (1) frequency of land-cover changes over a period of time, (2) the sequence of land-cover types, (3) the time span over which each land-cover type extends, and (4) the magnitude of difference between land-cover types. We synthesize the impacts of these four components on ecological communities, showing that frequent land-cover changes are likely to favor species that are habitat and dietary generalists. Greater attention to the complex dynamics of land-cover changes is critical for a better understanding of the future impacts that human-generated land-use changes will have on global biodiversity.
    Full-text · Article · May 2014 · Frontiers in Ecology and the Environment
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    David M Watson · Mathew Herring

    Preview · Article · Jan 2014 · Proceedings of the Royal Society B: Biological Sciences
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    ABSTRACT: Five years of research on interrelationships between fauna use of almond plantations and native vegetation in north-western Victoria shows that almond plantations have a strong influence on fauna dynamics and in some cases may provide important habitat for threatened species.
    No preview · Article · Jan 2014 · Ecological Management & Restoration
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    Full-text · Article · Dec 2013 · Conservation Biology
  • David M Watson · John Rawsthorne
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    ABSTRACT: Many plants use birds to disperse their propagules, but mistletoes are especially reliant on their services. As aerial parasites, mistletoe seeds need to be deposited upon branches of suitable hosts, and mistletoe specialist frugivores (from eight different avian families) have long been regarded as their coevolved dispersers. Like the pioneer Johnny 'Appleseed' Chapman who established nurseries that helped open up land for settlement, these birds are considered benevolent dispersers of this keystone resource and often invoked as illustrative examples of mutualistic interactions. We have compared recent research on these specialists with studies of other birds with broader diets (generalists) which also disperse mistletoe seed. Rather than mutualists, we suggest that mistletoe specialist frugivores are better considered exploitative, with multiple lineages evolving independently to capitalize on this reliable, nutritious resource. Although mistletoe specialist frugivores are quantitatively important seed dispersers in some regions, their specialized diet restricts them to areas with high mistletoe densities, resulting in contagious dispersal patterns. By intensifying existing infections, mistletoe specialist frugivores increase their own medium-term food security-akin to market gardeners profiting from intensive cultivation. Exploring the ecological and evolutionary implications of this proposition, we evaluate the consequences of different dispersal patterns on mistletoe fitness and highlight the neglected role of dietary generalists in the stabilization of plant-animal interactions.
    No preview · Article · Jun 2013 · Oecologia
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    Laurence P. Barea · David M. Watson
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    ABSTRACT: 1. Nest-site location is a critical component of habitat preference in birds, reflecting a balance between minimizing the likelihood of nest predation while maximizing access to nutritional resources. While many studies have demonstrated the influence of predators in nest-site selection, few studies have explicitly quantified nutritional resources or considered the interacting effects of predation and food availability in determining nest survival. 2. The painted honeyeater Grantiella picta is a mistletoe-specialist frugivore, with fruit from grey mistletoe Amyema quandang representing the main food source for breeding adults and nestlings. Previous work demonstrated that painted honeyeaters prefer to place their nests within mistletoe substrates. Here, we measured the outcome of 63 nests over two years, relating survival to various structural and resource-based variables to discern whether nests placed in mistletoes were more likely to succeed. 3. Twenty-one nests survived the 33 day nest period, with 35 of the 42 failed nests predated. While few significant differences were discerned between successful and unsuccessful nests in terms of nest tree or surrounding habitat, nest substrate emerged as the most important predictor of nest fate. Survival of nests in mistletoe was 16·6% across a 33 day active nest period compared with a mean of 43·1% for nests in other substrates, a difference consistent across both years. 4. Rather than having a positive effect on nest outcome (via access to nutritional resources), proximity to mistletoe had a marked negative effect, with nests in mistletoe suffering a predation rate 2·6 times higher than nests elsewhere. Rather than predators targeting mistletoe clumps, we suggest that this pattern arises from other species visiting fruiting mistletoe clumps, opportunistically predating the nest contents and disturbing attending parents. We interpret this finding as evidence that the painted honeyeater may be caught in an ecological trap; the cues used to select nesting locations are a poor predictor of success.
    Full-text · Article · Jun 2013 · Functional Ecology
  • David M. Watson
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    ABSTRACT: Mistletoes rely on birds for seed dispersal, but the presumed importance of mistletoe-specialist frugivores has not been critically examined nor compared with generalist frugivores and opportunistic foragers. The contribution of these three groups was compared directly by quantifying bird visitation to fruiting mistletoe plants ( Oryctanthus occidentalis: Loranthaceae) at Barro Colorado Island, Panama, and by comparing these results with proportions calculated from other empirical studies of mistletoe visitation conducted elsewhere. After more than 100 h of timed watches, 23 bird species were recorded visiting eight heavily infected host trees ( Luehea seemannii: Tiliaceae). Eight of these species visited mistletoe, of which five (all tyrannids) consumed mistletoe fruit. Although two mistletoe specialist frugivores ( Tyrannulus elatus and Zimmerius vilissimus) removed most fruit (73%), more than a quarter was consumed by one generalist frugivore ( Mionectes oleagineus) and two opportunists ( Myiozetetes cayanensis and Myiozetetes similis). Post consumption behaviour varied: the specialists flew from mistletoe to mistletoe, the generalist rested in the subcanopy and understory, and the opportunists spent most time hawking insects and resting high in the canopy. Integrating these data with previous work, the dietary specialization, short gut passage rate and strict habitat preferences of mistletoe specialists suggests that their services relate primarily to intensification and contagious dispersal, while species with broader diets are more likely to visit uninfected trees and establish new infections. The presumed importance of mistletoe-specialist frugivores was not supported and mistletoes are considered to be comparable to many other bird-dispersed plants, relying on both specialist and generalist frugivores, while opportunists may be disproportionately important in long-distance dispersal.
    No preview · Article · Mar 2013 · Biotropica
  • Anna E. Burns · David M. Watson
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    ABSTRACT: Mistletoes are a functional category of plants, defined as shrubby, aerial hemiparasites which depend on their host plants for water and mineral nutrition. Although three aberrant species (all in monotypic genera) are root parasitic, mistletoes are stem parasites, attaching to their hosts via specialized organs called haustoria. Mistletoes belong to the order Santalales and are arranged in the families Loranthaceae, Viscaceae, Misodendraceae, and Santalaceae, with the great majority of species belonging to the first two families (Nickrent et al. 2010). Although some species regularly parasitize lianas and other mistletoes, most species are dependent on trees and shrubs as principal hosts. The more than 1,500 species worldwide live in diverse habitats from rainforest to semiarid woodlands and are absent only from habitats devoid of woody hosts (e.g., polar, alpine and desert environments). Mistletoes are an important food source and nesting site for many birds and mammals (Watson 2001; Cooney et al. 2006; Mathiasen et al. 2008) and have a positive effect on the diversity and distribution of vertebrate animals in a range of habitats (Mathiasen et al. 2008; Watson 2002). By comparison, the ecological interactions between mistletoes and invertebrates—particularly arthropods—are poorly known. Unlike birds and mammals—long-lived and highly mobile animals that visit mistletoes periodically—many insects live their entire lives within mistletoe clumps, completely dependent on them for food and shelter. In this contribution, we summarize recent research on mistletoe-dependent arthropods, contrasting the extreme specialism exhibited by herbivorous groups, with lower substrate specificity (and greater dependence on structural complexity) displayed by predatory taxa. Rather than simply a subset of the biota found in the host canopy, we demonstrate that arthropods in mistletoes represent discrete and complementary assemblages, hitherto overlooked islands within a sea of forest and woodland treetops. Finally, we consider these findings in terms of the threats facing many forested systems, demonstrating the utility of mistletoe-dependent arthropods as sensitive indicators of overall forest health and ecosystem integrity.
    No preview · Chapter · Jan 2013
  • Helen C. Stevens · David M. Watson
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    ABSTRACT: Declines of formerly widespread bird species are being increasingly reported, with habitat loss, agricultural intensification and reduced rainfall frequently implicated. We report on temporal changes in the occurrence of birds over 21 years within continuous forest in the Warrumbungle Mountains to evaluate the influence of rainfall variability on changes in the abundance of birds and species occurence. During this period, six common insectivores declined significantly (Superb Fairy-wren, Malurus cyaneus; White-throated Gerygone, Gerygone albogularis; Grey Shrike-thrush, Colluricincla harmonica; Rufous Whistler, Pachycephala rufiventris; Grey Fantail, Rhipidura albiscapa; Eastern Yellow Robin, Eopsaltria australis). Rainfall significantly predicted the abundance of 13 of the 25 most common species, with the rainfall period of both July-December of the previous year and the combined effects of six years of January-June rainfall correlated with changes in the abundance of birds. Prolonged drought has likely driven food shortages (especially of litter-dwelling arthropods), with changes in avian community composition reflecting changes in food availability. Thus, avian declines in southern Australia may reflect the combined effects of habitat fragmentation and other landscape-scale changes in concert with larger-scale ecological processes driven by decreased rainfall. Improved linkages between forested and agricultural landscapes at the regional scale are needed to buffer against local fluctuations in resources.
    No preview · Article · Jan 2013 · The Emu: official organ of the Australasian Ornithologists' Union
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    ABSTRACT: 1. Expert knowledge is used routinely to inform listing decisions under the IUCN Red List criteria. Differences in opinion arise between experts in the presence of epistemic uncertainty, as a result of different interpretations of incomplete information and differences in individual beliefs, values and experiences. Structured expert elicitation aims to anticipate and account for such differences to increase the accuracy of final estimates. 2. A diverse panel of 16 experts independently evaluated up to 125 parameters per taxon to assess the IUCN Red List category of extinction risk for nine Australian bird taxa. Each panellist was provided with the same baseline data. Additional judgments and advice were sought from taxon specialists outside the panel. One question set elicited lowest and highest plausible estimates, best estimates and probabilities that the true values were contained within the upper and lower bounds. A second question set elicited yes/no answers and a degree of credibility in the answer provided. 3. Once initial estimates were obtained, all panellists were shown each others’ values. They discussed differences and reassessed their original values. Most communication was carried out by email. 4. The process took nearly 6 months overall to complete, and required an average of 1 h and up to 13 h per taxon for a panellist to complete the initial assessment. 5. Panellists were mostly in agreement with one another about IUCN categorisations for each taxon. Where they differed, there was some evidence of convergence in the second round of assessments, although there was persistent non-overlap for about 2% of estimates. The method exposed evidence of common subjective biases including overconfidence, anchoring to available data, definitional ambiguity and the conceptual difficulty of estimating percentages rather than natural numbers. 6. This study demonstrates the value of structured elicitation techniques to identify and to reduce potential sources of bias and error among experts. The formal nature of the process meant that the consensus position reached carried greater weight in subsequent deliberations on status. The structured process is worthwhile for high profile or contentious taxa, but may be too time intensive for less divisive cases.
    Full-text · Article · Oct 2012 · Methods in Ecology and Evolution
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    David M Watson · Matthew Herring
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    ABSTRACT: Various entities have been designated keystone resources, but few tests have been attempted and we are unaware of any experimental manipulations of purported keystone resources. Mistletoes (Loranthaceae) provide structural and nutritional resources within canopies, and their pervasive influence on diversity led to their designation as keystone resources. We quantified the effect of mistletoe on diversity with a woodland-scale experiment, comparing bird diversities before and after all mistletoe plants were removed from 17 treatment sites, with those of 11 control sites and 12 sites in which mistletoe was naturally absent. Three years after mistletoe removal, treatment woodlands lost, on average, 20.9 per cent of their total species richness, 26.5 per cent of woodland-dependent bird species and 34.8 per cent of their woodland-dependent residents, compared with moderate increases in control sites and no significant changes in mistletoe-free sites. Treatment sites lost greater proportions of birds recorded nesting in mistletoe, but changes in species recorded feeding on mistletoe did not differ from control sites. Having confirmed the status of mistletoe as a keystone resource, we suggest that nutrient enrichment via litter-fall is the main mechanism promoting species richness, driving small-scale heterogeneity in productivity and food availability for woodland animals. This explanation applies to other parasitic plants with high turnover of enriched leaves, and the community-scale influence of these plants is most apparent in low productivity systems.
    Preview · Article · Jul 2012 · Proceedings of the Royal Society B: Biological Sciences